Conventional photopolymerizable compositions have been developed with organic solvent developers. However, organic solvents are generally expensive, toxic, and combustible. Moreover, use of organic solvents entails enormous cost for industrial hygiene and countermeasures against environmental pollution. Photopolymerizable compositions which can be developed without using any organic solvents are therefore in great demand. In general, what determines solubility and other properties of photopolymerizable compositions is the binder component used therein.
Representative photopolymerizable compositions developable with an alkaline aqueous solution include those described in Japanese Patent Publication No. 14065/60 (polymers containing oxygen in the side chain are used as binder; hereinafter the compounds in the parentheses are binders used in the respective compositions), Japanese Patent Publication No. 32714/71 (corresponding to U.S. Pat. No. 3,458,311) (methyl methacrylate/methacrylic acid copolymers, etc.), Japanese Patent Publication No. 34327/79 (corresponding to U.S. Pat. No. 3,804,631) (methyl methacrylate/2-ethylhexyl methacrylate/methacrylic acid terpolymers, etc.), Japanese Patent Publication No. 38961/80 (corresponding to U.S. Pat. No. 3,953,309) (styrene/mono-n-butyl maleate copolymers, etc.), Japanese Patent Publication No. 33413/81 (corresponding to British Patent 1,425,423) (ethyl methacrylate/ethyl acrylate/methacrylic acid terpolymers, etc.), Japanese Patent Publication No. 25957/79 (styrene/methyl methacrylate/ethyl acrylate/methacrylic acid tetrapolymers, etc.), Japanese Patent Application (OPI) No. 99810/77 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application") (corresponding to U.S. Pat. No. 4,139,391) (benzyl methacrylate/methacrylic acid copolymers, etc.), Japanese Patent Publication No.12577/83 (corresponding to U.S. Pat. No. 3,930,865) (acrylonitrile/2-ethylhexyl methacrylate/methacrylic acid terpolymers, etc.), Japanese Patent Publication No. 6210/80 (corresponding to U.S. Pat. No. 4,273,857) (methyl methacrylate/ethyl acrylate/acrylic acid terpolymers, or styrene/maleic anhydride copolymer partially esterified with isopropanol), Japanese Patent Application (OPI) No. 1142/83 (methyl methacrylate/methacrylic acid/2-ethylhexyl acrylate terpolymers or methacrylic acid/methyl methacrylate/2-ethylhexyl acrylate/n-butyl methacrylate tetrapolymers), Japanese Patent Application (OPI) No. 159743/85 (corresponding to U.S. Pat. No. 4,629,680) (cyclohexyl methacrylate/methyl acrylate/methacrylic acid/acrylic acid tetrapolymers), Japanese Patent Application (OPI) No. 258539/85 (corresponding to U.S. Pat. No. 4,629,680) (benzyl methacrylate/methyl acrylate/methacrylic acid/acrylic acid tetrapolymers), Japanese Patent Application (OPI) No. 169829/86 (corresponding to U.S. patent application Ser. No. 824,343) (benzyl methacrylate/methacrylic acid/acrylic acid terpolymers), and Japanese Patent Application (OPI) No. 213213/86 (benzyl acrylate/methyl methacrylate/methacrylic acid terpolymers).
Although these known alkali-developable photopolymerizable compositions have advantages in some applications, they involve disadvantages as set forth below when used in the production of photoresists.
Printed circuit boards can be produced by laminating a photosensitive solid film on a base, e.g., typically a copper-clad laminate base, under pressure as disclosed in Japanese Patent Publication No. 25231/70 (corresponding to U.S. Pat. No. 3,469,982). Photopolymerizable compositions suited for this technique are required to have well-balanced properties, such as developability, releasability (strippability) of a resist (the resist in a polymerized state should have resistance to an etching solution or a plating solution), low tackiness, high adhesion to a base, and flexibility. In this connection, the above-recited known polymerizable compositions have one or more disadvantages of excessive tackiness or brittleness, insufficient adhesion to a base or resistance to swelling for providing an image of high resolving power, long development time, and the like.
In addition, a dry film resist is sought which provides a resist line image faithful to the original and with high resolving power in order to satisfy the recent demand for high density printed wiring, but conventionally known photopolymerizable compositions developable with an alkaline aqueous solution cannot satisfy this requirement due to their lack of resistance to swelling by a developing solution and adhesion to a base.